Heat exchangers, of which there are a plurality of types, are employed to heat or cool a liquid product. Using, for example, water vapour or water at different temperatures, it is possible to heat or cool to the desired level a product which is preferably in liquid form. Heat exchangers come into use in various process industries and are also common phenomena in food industries such as dairies and juice factories.
One well-known type of heat exchanger is the so-called shell-and-tube heat exchanger which consists of one or more heat exchanger elements which are interconnected together to form a flow system. The heat exchanger elements consist of one or more heat transfer tubes surrounded by an outer shell or jacket tube. The heat transfer tubes are interconnected with one another to form product flow inserts which in turn are interconnected by means of product pipe bends in order to circulate the product which is to be heated or cooled, depending upon the process for which the heat exchanger is employed. The heat exchanger tubes are enclosed in shell or jacket tubes which also enclose the heat transfer medium which may consist of water at different temperatures, water vapour or other types of liquids or gases. One type of shell-and-tube heat exchanger is described in Swedish Patent Specification SE 501908.
A shell-and-tube heat exchanger in accordance with the foregoing description may be employed for treating liquids containing large particles or fibres, such as, for example, orange juice with relatively long fibres. Uncut orange fibres may be as much as 25 mm in length. When the fibrous liquid is caused to pass through the product flow inserts, the liquid from the product pipe bends must be distributed via a baffle plate into the individual heat transfer tubes. In such instance, it is a common occurrence that the fibres "hang" on the edge, at the entry to the heat transfer tubes and accumulate here. Trials have shown that, when the pressure increases in such an event, a complete accumulation of fibres is often flushed out after a while, whereafter the accumulation begins again and this results in an uneven distribution of the fibres in the liquid. Extreme accumulations of fibres may also give rise to productional disruptions and problems involved in cleaning. Large particles may also contribute in forming plugs in the inlets to the individual heat transfer tubes.
One method of obviating these problems is to increase the diameter of the heat transfer tubes so that the fibres and particles may more easily gain access. An extreme solution of this method is the monotube which, however, gives rise to poor heat transfer coefficient, long tubes and long process times. It is therefore desirable to keep the diameter of the heat transfer tubes as small as possible, for large particles heat transfer tubes in conventional shell-and-tube heat exchangers must be selected with an inner diameter which is between 2 and 2.5 times larger than the particles which are to pass through these tubes, which thus reduces the heat transfer coefficient.